At present, using an unlicensed frequency band (for example, 2.4 GHz and 5.8 GHz) to extend a using frequency of a wireless cellular system is started to be considered for the wireless cellular system. Two methods are mainly adopted, i.e. License Assisted Access (LAA) and Long Term Evolution (LTE)/Wireless Fidelity (WiFi) aggregations. The two aggregation methods mainly have the following characteristics: (1) an aggregation resource belongs to an unlicensed frequency band, and is only used as an auxiliary frequency band for an ordinary licensed frequency band; and (2) use of the unlicensed frequency band is not only limited by scheduling of a base station, but also limited by a load of the frequency band, and namely, the unlicensed frequency band may be used through a competition mechanism. Therefore, compared with the licensed frequency band, an access time of a terminal is required to be as short as possible such that the resource of the unlicensed frequency band may be fully utilized within a limited time and a utilization rate of the resource may be increased.
At the present stage, an unlicensed frequency band still exists only as a supplement for a licensed frequency band. For example, in an LAA technology, the unlicensed frequency band may adopt an LTE working mode, but may exist only as a secondary carrier for the licensed frequency band. In the future, LAA may adopt an independent working mode like a Wireless Local Area Network (WLAN). In such case, when a terminal has no data connection and thus is in an idle state, the terminal may camp in a cell using the licensed frequency band or the terminal may camp in a cell using the unlicensed frequency band. However, for accessing to the unlicensed frequency band cell, it is necessary to use a Listen Before Talk (LBT) mechanism for monitoring and detecting a wireless channel and after transmission for a certain period of time in case of successful competition, return to a monitoring state to continue monitoring and completing for the channel like the WLAN. Therefore, performance, such as time delay, packet loss rate and the like of access of the terminal cannot be ensured like the licensed frequency band cell. In spite of this, the unlicensed frequency band also has the advantages of rich frequency band resources, larger bandwidth and the like, and the terminal may flexibly select to access an unlicensed frequency band channel having a better channel condition. Therefore, how to enable a terminal equipment to flexibly camp in a licensed frequency band cell and an unlicensed frequency band cell is a problem to be solved at present.